1. Field of the Invention
The present invention relates to pyridazinone derivatives or pharmacologically acceptable salts thereof which exhibit an inhibitory activity against platelet aggregation and are thus useful for the treatment of circulatory disorders such as cerebral infarction or myocardial infarction.
2. Related Art
In recent years, thrombosis has been considered to be a major cause for circulatory disorders such as cerebral infarction or myocardial infarction. For the prevention and treatment of such disorders, a treatment has been widely spread in the clinical field, using plate aggregation inhibitors which lower the function of platelet. However, the history is relatively new and it has been expected to develop excellent drugs of this category.
It is shown in Japanese Patent Application KOKAI (Laid-Open) Nos. 63-30187 and 2-256668, European Patent Disclosure Nos. 0275997 and 0376079, and U.S. Pat. Nos. 4,978,665 and 5,011,839 that pyridazinone derivatives show a strongly antagonistic activity against SRS-A (slow reacting substance of anaphylaxis). However, these prior publications are silent on a platelet aggregation inhibiting activity. Compounds shown in Japanese Patent Application KOKAI No. 5-112454 and International Patent Application KOKAI No. W091/16314 are already known as platelet aggregation inhibitors but the effect is not satisfactory.